Defining your external subsystems to IMS

In order for IMS to initiate contact with an external subsystem, you must add a subsystem member (SSM) to the IMS PROCLIB data set for each external subsystem with which IMS communicates.

This SSM contains an entry for each external subsystem with which IMS communicates. In the case of Db2 for z/OS® with several possible definitions for the same Db2 for z/OS system, the member contains one access for Java™ regions in IMS and the other for other region types. When defining Db2 for z/OS databases, this member contains one entry for each Db2 for z/OS subsystem, or an entry that defines a group of Db2 for z/OS subsystems.

You can also establish simultaneous access to the same Db2 for z/OS subsystem if the IMS PROCLIB data set member contains a definition for both connections.

Define the SSM PROCLIB member (or members) using the IMS PROCLIB data set that is allocated before Stage 2 of IMS system definition and the z/OS utility IEBUPDTE. The first 1 - 4 characters of this PROCLIB member's name must match the IMSID, as specified by the IMSID parameter on the IMSCTRL macro statement, or it must be overridden using the execution parameter IMSID=. The last four positions represent any unique installation-defined identifier. This identifier is appended to the IMSID to construct the member name.

After defining the SSM PROCLIB member, before you can use it you must:

Insert a DD statement for IMS PROCLIB with the DD name PROCLIB in the step execution JCL.
Specify the correct PROCLIB member on the EXEC statement parameter SSM= or on the /START SUBSYS SSM command.

Each entry within the PROCLIB member consists of a blocked or unblocked 80-character record. Information for each record begins in position 1 of the record.

An SSM PROCLIB member can contain either positional-format statements in a fixed order, or keyword-format statements in a semi-fixed order.

Restriction: A single subsystem definition cannot use both positional and keyword parameters simultaneously.

Positional format

Fixed parameter format. Keywords are not allowed. Values must be entered in the following order: ssn, lit, esmt, rtt, reo, crc.

For example,

V10A,SYS1,DSNMIN10,RTTDB2A,R,-

Keyword format

Keyword-only, and must begin with SST=. After SST=, most values can be specified in any order:

SST=,SSN=,LIT=,ESMT=,RTT=,REO=,CRC=,RLA=

For example,

SST=DB2,SSN=DB21,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-,RLA=Y

If COORD is specified, only SST= and SSN= may also be specified; all other keywords are ignored:

SST=,SSN=,COORD=

For example,

SST=DB2,SSN=DB21,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-

SST=DB2,CRC=-,REO=R,ESMT=DSNMIN10,LIT=SYS1,SSN=DB21

SST=MQ,SSN=SYS3,LIT=MQM3,ESMT=CSQQESMT

SST=DB2,SSN=V71A,COORD=RRS

The SSM member can contain two keyword-only parameters, SST= and COORD=. These parameters cannot be specified positionally. The COORD= parameter specifies the type of resource coordination controller, such as RRS. The SST= parameter specifies the type of external subsystem.

On the SST= parameter, the valid external subsystem types are:

DB2: Db2 for z/OS
MQ: IBM® MQ
WOLA: WebSphere® Optimized Local Adapter

Attention: If you define the subsystem in positional format, IMS displays DB2 as the ESS type in both command responses and DFS messages even if you are using MQ or WOLA.